Hearing-aid sound transducer



Jan. 29, 1963 H. FENER HEARING-AID SOUND TRANSDUCER 2 SheetsSheet 1 Filed Oct. 30. 1959 Jan. 29, 1963 H. FENER HEARING-AID scum: TRANSDUCER 2 Sheets-Sheet 2 Filed Oct. 30. 1959 United States atent This invention relates to miniature sound transducers, in particular to microphones and earphones used in-eyeglass-type hearing aids and behind the ear models.

An object of this invention is to provide a sound transducer substantially smaller in size than the smallest units previously availablev commercially and having comparable response and sensitivity.

"Still another object is to provide such a unit-which though extremely smallin sizeis nonetheless relatively easy .and inexpensive to fabricate and assemble to the precise tolerances. required.

A more specific object is to provide a miniaturemicrophone or earphone which through extremely small is very .eflicient and reliable.

These and other objects will impart he pointedoutin and in part understood from the "following description.

The development of ultra-small transistor. amplifiers 25 lead in turn 'tofithe development in recentyears of phones or earphones, which have been commercially available are .very delicate and complicatedand though small by other standards are usually thebulkiest elements .in .the entire unit. The size of these previouslyav-ailable microphones and earphone-s is such that the spectacle frameshousing them have had to be enlarged substantially giving them an unavoidable and undesirable'bul- .bous appearance. The present invention provides .a microphone and a companion earphone which are only. about h-alfithe size of previous units of comparable high performance. The sound transducers provided by the invention contain considerably'fewer parts than previous ones andv are very e'fficient and reliable.

In accordance with the invention, in one specific embodiment thereof, there is provided a miniature microphone having a tongue-likearmature of magnetic material With one end positionedgbetween two smallpermanent magnets held by a stationary U shaped polepiece. The other end of the Jarmature is. encircled by a stationary electric coil and near the center of the armature isplaced a drive pin which extends "at right angles 'to an acoustic diaphragm. These parts are arranged to obtain maximum effectiveness of .the'magnetic field-gener-atedby the magnets. There is very little stray field, and this is further minimized by enclosing the structure in a closely fitting case of ,magnetic materiahsuch as nickel steel. .TBecause veach unit. isthus magnetically as well as physically enclosed, the troublesome problem of .mutual-coupling between a, microphone and a ..closely spaced earphone is efifectively eliminated.

The-drive pin in thismicrophone unit is .in accordance with anaspect oftheinvention made readily adjustable 1111111353 50 that the frequency response of the unit can .be varied as desiredinthetcourse of production. ,-As

Patented an.-.29, 1-963 '2 will .iappear, other mechanical .we'ight adjustments can also be made. .The .drive pin is spring-fitted over the armature to give a secure but pivoting connection to'it .and vthe other endoflhe ,drive pin .is cemented :to the 5 center part of the diaphragm. Thelatter comprisesa thin flexible sheet of plastic film, such as :mylar, cemented .along its edges to the rimof lthecase and having cemented to. its center part a reinforcing sheet of .thin aluminum. To facilitate the cementing ,ofthis .plasticlayer onto the casing, .the layer iswinitia'llymadelarger thannecessary sothatfit overlapsthe top edge of the casing. ,After this 'layer'h-as'been cemented to the dge,'the excess plastic material is trimmed. off ,Witha razor blade.

Thecentral and majorpart of the diaphragm behaves as a rigid piston whose vibratiomunde'r' the excitationof impinging sound waves is transmittedthrough [the drive pin tothe armature, the motion of, which generatesin the coil an electric voltage corresponding to the sound waves. The stitfening sheetof aluminum on the diaphragm' is uniquely shaped. and has a raised circular or oval rib .Whichgives added rigidity and which in conjunction with the plastic filmlbeneath and suitable vent holes serves as a soundtransrnission tube of considerable length conneoting'the'inside of the case. and rear of the diaphragm-with the front of the diaphragm and out side. Thus, part of the sound impingingon the, front of thediaphragm travels throughthis tube to the rearv side "of the diaphragm and, 'by proper choice of the length -of the1tube, arrives "at the ear in proper phase to reiniforce theifront sound waves in their action on the diraphragm.

{The ;U-:shaped. pole-piece of ;the unit is .uniquely ;mounted in r,elat iontothe armature 'sothat the various parts can be readily assembled and thengiven' afinal adjustment, made guicklyand easily from'the outside, to extpemely precise' toleranceslof the order of a'few million-ths-of:an inch). This isdone'with the unit connected in-its actual electrical circuit environment and is 40 accomplished without alfecting the acoustic "sensitivity of *the unit. As ,a-resnlt, quantity-production of these units is'consider albly simplified and much tighter quality f c'ontrol achieved in spite of the facts-hat'"these-units; are only about halt the size of previous -onesgo'f comparable 5 T Quality.

'The-unitjustdescribed is made'into anearphone simply by modifying the sound transmission tube in the acoustic di aphra-gm. jNow, in an 'earph'one unit it may --be desirable to have its'frequency response complement that-ofia companion-microphone. Very=fine adjustments in this responsecan be made by varying the --weight -of the drive pin 'aswas mentioned and also :by changing :the mass ot;the idiaphragm. A coarser adjustment, as illustrated in a second embodiment of the invention, {is

obtained by mounting 5 the: energizing :magnets in 1 the: unit :on the endof theLarmaturerLather than on the fiXed U- shaped. poleapiece. lAdditionally, and .this. -arrangementiis .;particularly suit-ablerfona-bone conduction'ltype'of unit, :the .electrie-co-il :can, also she -.mounted I on; the armature.

-Azbettenunderstanding-of. the.inventiontogether-with:a

'. ifuller :appreciation of .its;ma.ny s advantages. vwill; best be .gainedxfrom. :a. study. of the following description given in :CDIlIlCIiOHzWi'th the: accompanying drawings-.rvherein:

. FIGURE '1 isa-perspective view of;an eyeglass 213.8-

.sernbly having -arhearingaidbuilt into the i'frame;

:FIGURE .2. is :a; greatlyeenlarged -:perspect-ive .viewof ia .-.micr,ophone,;embodying features of the invention .and .;usableinqa hearingzaid as shown-imFIGUREl;

. FIGURE 3 isadongitudinal sectionrview.taltengasjin- FIGURE: .4 is;:an end view .taken aasiindieate'd :by. lines -.4 ..;4 ,in .EIGURE;2;

3 FiGURE 5 is a further enlarged view of a portion of the drive pin; and

FIGURE 6 is a view similar to FIGURE 3 but showing an earphone embodying features of the invention.

The eyeglass assembly 10 shown in FIGURE 1 comprises a frame 12 having right and left ear pieces 14 and 16 adapted to fit over a persons ears to hold the frame in place. Mounted within ear piece 14 is a hearing-aid including a microphone 18 and an earphone 2t). Extendture inside. This includes an, armature having a tonguelike portion 28 extending from the right end of the easing and a base portion 30 extending underneath tongue 28 slightly above the bottom of the casing. The right end of the armature is rigidly supported against the inner vertical end of the casing by a tab 32 welded to the armature at 34 and to the casing at 36. The left end of base .30, see also FIGURE 4, rests upon and is welded to dimples 38 at opposite corners of the casing.

Fastened onto base somewhat to the right of its left end is a U-shaped pole-piece 40 whose legs extend, respectively, above and below the left end of tongue 28. This pole-piece supports the permanent magnets 42 and 44 on opposite sides of the tongue of the armature, the north pole of one magnet facing the south pole of the other, the field generated by the magnets being generally perpendicular to tongue 28. These magnets should be of high efiiciency material and preferably should have high A.C. permeability as well. An acceptable material is Alnico V or VI.

The right end of tongue 28 is encircled but not touched by an electric coil 46 which is supported on base 30. The two ends of this coil are connected to terminals 50 and 52 extending through casing 26 and insulated therefrom by an insulator strip 54. Vibration of the tongue in the .magnetic field of magnets 42 and 44 generates a corre- "sponding voltage in coil 46, as Will be understood by those skilled in the art. The coil46 signal voltage is then amplitied and applied to earphone 20 by conventional amplifier means (not shown) to reproduce the original sound at suitable volume.

Positioned between coil 46 and pole-piece 40 and springfitted onto tongue 28 is a drive pin 56 which extends at right angles to an acoustic diaphragm 58. During as- '64 and plastic layer 62. The right end of oval 66 is vented by a front opening 68 through metal layer 64 and the left end is vented by a rear opening 70 through plastic layer 62. Thus a sound transmitting tube comprising two portions of oval 66 in parallel extends from the front to the rear opening. The length of this tube can be varied in production, as desired, by changing the position of openings 68 and 70*. To make this tube twice as long, for example, opening 70* can be placed closely adjacent opening 68 with an air seal inside oval 66 in the short length between the openings. Thus, sound will have to travel effectively entirely around oval 66 to go from opening 68 to opening 79. This simple way of adjustment of the length of the sound transmission tube permits considerable adjustment of the frequency response characteristics of the microphone and is a very desirable production aid. The sound transmission tube does not take up valuable space inside casing 26 and it does not complicate fitting or assembly of the parts. It thus represents an important improvement over prior constructions.

The top of the unit is provided with a dished cover 72 which fits snugly onto casing 26 and encloses the diaphragm. The center of the cover is pierced with an open ing F8 which permits sound waves to reach the diaphragm.

Pole-piece 40 and the tongue and base portions of the armature provide a generally continuous magnetic loop for the flux produced by magnets 42 and 44. The only air gaps in this circuit are the first one between magnet 42 and the upper side of tongue 28 and the second one between magnet 44- and the lower side of tongue 28, both gaps being relatively short. Now, in order to generate a relatively large voltage in coil 46 for a given up and down movement of tongue 28, which movement may be only a few millionths of an inch, the armature is made of an iron alloy having a very high permeability such as mu metal. Since this material magnetically saturates easily, it is necessary that tongue 28 be adjusted to an at-rest position between magnets 42 and 44 such that the net steady-state flux through it is as low as possible. However, each time mu metal is bent beyond its elastic limit,

. it loses its desirable magnetic properties, and must be sembly of these elements, the drive pin is pushed onto the tongue 28 of the armature and grips it (see FIGURE 4) on opposite sides with a jaw-like spring action. This 'preventsthe drive pin from shifting laterally on the armature but permits it to pivot slightly. With the drive pin extending upward from the armature as shown, the diaphragm is then placed on the top edge of the casing and cemented to it, the end of the drive pin extending into a inch thick mylar, whose edges are cemented to casing 26,

-and a somewhat thicker, stiff layer 64 of metal or the like,

such as .002 inch thick aluminum, cemented to it. The

side edges of the latter are close to but separated somewhat from thetop edge of the casing thereby permitting relatively very free vibration of the rigid center of the diaphragm. The center part of layer 64 is raised in an oval or race-track configuration 66 which adds further rigidity .to the diaphragm without increasing its weight and which provides a hollow spacebetween metal layer annealed at elevated temperature to regain them. Also, as a practical matter it is impossible during assembly of the unit to position the tongue portion of the armature in exactly the right position between magnets 42 and 44. To permit simple and rapid adjustment of the relative position of tongue 28 while at the same time avoiding the difiiculty, attendant upon bending mu metal, the portion of the armature base 30 to the left of pole-piece 40, which constitutes an extension 74, is made accessible from outside the casing through a rectangular window 76 (see FIGURE 4) between dimples 38. Thus by inserting a suitable tool below or above extension 74, it can be bent up or down thereby vertically moving pole-piece 49 while tongue 28 remains stationary. This provides a very simple and easy way to center the tongue of the armature which, if desired, can be carried out while the microphone is connected in its actual circuit environment. Any direct current which in the circuit would be flowing in coil 46 and which would otherwise cause an unbalancedsteady-state flux in the tongue of the armature can thus also be compensated for by this final mechanical adjustment. Since extension 74 is outside the magnetic circuit of the armature, bending it beyond its elastic limit to make this adjustment does not impairthe magnetic properties of the armature which, though its base 39 is deflected slightly, is not bent beyond its elastic limit. After the adjustment has been made window 76 is sealed.

Because the reluctance of the magnetic circuit is low, and by virtue of the placement of the armature and polepiece as shown with magnets on each side of the tongue of the armature, substantially improved efficiency for a given strength of magnet is obtained. This means, conversely, that for a given sensitivity, this unit can be substantially smaller than previous ones.

therreduced by :casing26, which is ferro-magnetic, and which-is in contact withthe sides .of armature base 30 and pole-piece 40. Magnets 42 and 44 are made slightly narrower than casing 26 to avoid direct shunting of their field.

As was mentioned, the weight of the moving mass of the armature canbe varied by adjusting the weight of drive .pin 56. "Ihis is advantageouslyaccomplished, as illustrated in FIGURE 5,'by fabricating the drive pin of -a thinihard layer 8%) of a non-magnetic metal such as beryllium copper plated with a thicker layer '82 ofa soft, malleable non-magnetic metal such as silver. 'Ihen simply by rolling the softer layer toadesired thickness the weight of the drive pin can be adjustedto a very'fine de- .gree. -By,stamping or blanking it out of a larger strip, the edges of-the drive pin will shearaway withthe softer :layer 82-beveled back as indicated .at 84 leaving-a -knifeedge, formed by the thin hard layer 82, in contact with the armature tongue.

FIGURE 6 shows an earphone 20 similar in construction to microphone 18. Here, sound waves are produced by the vibration of a diaphragm 90 which is identical to diaphragm 58 except that the diaphragm mass is changed and oval track 66 is generally lengthened; also the sound transmission tube is adjusted in length to give the desired bass frequency response. The sound waves so produced are conducted through tube 22 to a persons ear. The moving mass of the tongue of the armature in this embodiment is greatly increased by mounting magnets 42 and 44, and if desired coil 46, on the tongue of the armature. To make this a balanced armature type bone conduction receiver, a further distribution of the masses and stifinesses allow this transducer to efficiently transfer energy to the mastoid bone behind a persons ear.

An actual microphone substantially identical to microphone 18 which has been built and successfully operated had over-all dimensions of /4 by /2 by /5 inch, contained 13 parts, and had effectively the same sensitivity and response as the smallest known commercially-produced prior unit, which unit contained 23 parts and had dimensions of /8 by /2 by Ms inch. FIGURES 2-4 herein were made from the actual microphone and show the positions and shapes of its various parts in enlarged scale.

The above description of the invention is intended in illustration and not in limitation. Various changes in the embodiment set forth may occur to those skilled in the art and may be made without departing from the spirit or scope of the invention as set forth.

What I claim is:

1. A miniature, high efficiency sound transducer comprising a box-like casing of magnetic material containing a U-shaped armature having one arm adjacent the bottom of said casing and the other arm somewhat above and parallel thereto, the web end of said armature being supported by said casing, a coil encircling a portion of the flux path of said armature near its web end, a U-shaped pole-piece having one arm affixed to the lower arm of said armature and its other arm above the free end of the upper arm of said armature, a pair of permanent magnets mounted on inner portions of said pole piece arms respectively above and below the free end of said upper armature arm, said magnets having relatively high permeability to alternating signal magnetic flux of the transducer and projecting permanent unidirectional magnetic flux directly into said free armature end, a drive pin attached to said upper arm of said armature near its center, and a diaphragm extending across the upper region of said casing, and being attached near its center to said drive pin.

2. A miniature, high efiiciency sound transducer comprising a box-like casing containing a U-shaped armature having one arm adjacent the bottom of said casing and the other arm somewhat above and substantially parallel J-thereto,3the web-"end of said armature: being supported by said casing, a coil encircling a portion of the fluxpath of said armature near its'web end, a U-shapedpole-piece having one arm affixed'to thelower arm of said armature and its other arm above the free end of the upperarm of said armature, a pairofpermanentmagnets mounted respectively aboveand below the free end of said upper armature arm, a drivepin attached to said upper arm of said armature near its center, av diaphragm extending across the upper region of said casing, and beingattached near itscenterto said drive pin, and wherein said casing is ofmagnetic material and has walls close to the sides of saidpole-piece.

' 3. Aminiature high efficiency-sound transducer comprising a'box-like casing 'containing a U-shapedarmature having onearm adjacent the bottom of fsaid casingiand the other arm somewhatabove and substantially parallel -'thereto, the webend'of said'armaturebeing supportedby said jcasing 'a coil encircling ajportion ,of the flux .path

of said armature near its web end, a U-shaped pole-piece having one arm afiixed to the lower arm of said armature and its other arm above the free end of the upper arm of said armature, a pair of permanent magnets mounted respectively above and below the free end of said upper armature arm, a drive pin attached to said upper arm of said armature near its center, a diaphragm extending across the upper region of said casing, and being attached near its center to said drive pin, and wherein the lower arm of said armature extends somewhat beyond the end of said pole-piece and is fastened at its outer end to said casing, said end being bendable from outside said casing to adjust the position of the free end of the said other arm of said armature with respect to the arms of said pole-piece.

4. A miniature sound transducer comprising a casing, an armature having a tongue-like portion supported at one end and extending as a cantilever generally parallel to the bottom of said casing, flux means including at least one permanent magnet and a magnetic pole-piece having arms respectively above and below the free end of said tongue-like portion, a coil encircling a portion of the fiux path through said armature and having a pair of output terminals, an acoustic diaphragm positioned opposite said armature and supported by said casing, and a drive pin connected between said tongue-like portion and said diaphragm, said armature having a base portion closely along the bottom of said casing, said pole-piece being mounted on said base portion with an extension thereof continuing beyond said pole-piece and accessible from outside of said casing, said armature being of an iron alloy which loses its desirable magnetic properties when bent too much, whereby bending of said extension to position said pole-piece relative to the free end of said tongue-like portion does not affect the magnetic properties of the portions of said armature in the alternating signal flux path of the transducer.

5. The transducer as claimed in claim 4 wherein said polepiece, armature, magnet and coil are a unitized assembly fastened at one end to said casing wall, said armature extension being fastened at the other end of said casing.

6. An improved electromagnetic sound transducer comprising a tongue-like armature of magnetic material, flux means including a pair of opposed pole faces and a surrounding cup-shaped casing of magnetic material, said pole faces being supported in side edge contact with said casing which also supplies a return path for at least some of the transducer alternating signal flux passing from one pole face to the other, said armature being fixed at one end in said casing and having a movable portion positioned between said pole faces, a small permanent magnet positioned between said pole faces near said armature, said magnet being recessed from contact with said casing, a signal coil encircling a portion of the flux path through said armature, and an acoustic diaphragm stretched over 7 said casing and connected to said armature to vibrate with it.

7. The transducer as claimed in claim 6 wherein'said magnet is fixed to the said movable portion of said armature. v

8. A miniature sound transducer comprising a housing of magnetic material, a generally U-shaped armature having two parallel arms, the web region of said armature being fastened to said housing, a pole piece having two opposed faces, said pole piece being fixed to the end region of one of said arms with its said faces on opposite sides of the end region of the other arm, at least one permanent magnet positioned between said faces, said pole piece having its side edges in contact with said hous ing and said magnet being spaced from contact with said housing to supply a return path for at least some of the transducer alternating signal flux passing from one pole face to the other, a coil encircling a portion of the flux 8 path through said armature, and a diaphragm mounted over said housing and connected to said armature.

9. The transducer as claimed in claim 8 wherein said magnet is fixed onto the said end region of said other arm of said armature.

References tlited in the file of this patent UNITED STATES PATENTS 1,573,739 ONei-ll Feb. 16, 1926 1,719,472 Holland July 2, 1929 2,582,942 Baker Jan. 22, 1952 2,692,918 Berger Oct. 26, 1954 2,966,558 Knowles Dec. 27, 1960 FOREIGN PATENTS 392,318 Great Britain May 18, 1933 625,274 France Apr. 23, 1927 1,052,458 Germany Mar. 12, 1959 1,133,358 France- Nov. 19, 1956 

1. A MINIATURE, HIGH EFFICIENCY SOUND TRANSDUCER COMPRISING A BOX-LIKE CASING OF MAGNETIC MATERIAL CONTAINING A U-SHAPED ARMATURE HAVING ONE ARM ADJACENT THE BOTTOM OF SAID CASING AND THE OTHER ARM SOMEWHAT ABOVE AND PARALLEL THERETO, THE WEB END OF SAID ARMATURE BEING SUPPORTED BY SAID CASING, A COIL ENCIRCLING A PORTION OF THE FLUX PATH OF SAID ARMATURE NEAR ITS WEB END, A U-SHAPED POLE-PIECE HAVING ONE ARM AFFIXED TO THE LOWER ARM OF SAID ARMATURE AND ITS OTHER ARM ABOVE THE FREE END OF THE UPPER ARM OF SAID ARMATURE, A PAIR OF PERMANENT MAGNETS MOUNTED ON INNER PORTIONS OF SAID POLE PIECE ARMS RESPECTIVELY ABOVE AND BELOW THE FREE END OF SAID UPPER ARMATURE ARM, SAID MAGNETS HAVING RELATIVELY HIGH PERMEABILITY TO ALTERNATING SIGNAL MAGNETIC FLUX OF THE TRANSDUCER AND PROJECTING PERMANENT UNIDIRECTIONAL MAGNETIC FLUX DIRECTLY INTO SAID FREE ARMATURE END, A DRIVE PIN ATTACHED TO SAID UPPER ARM OF SAID ARMATURE NEAR ITS CENTER, AND A DIAPHRAGM EXTENDING ACROSS THE UPPER REGION OF SAID CASING, AND BEING ATTACHED NEAR ITS CENTER TO SAID DRIVE PIN. 